The Absence of Adiabatic Contraction of the Radial Dark Matter Profile in the Galaxy Cluster A2589

Abstract

We present an X-ray analysis of the radial mass profile of the radio-quiet galaxy cluster A2589 between 0.015 and
\n0.25rvir, using an XMM-Newton observation. Except for a 16 kpc shift of the X-ray center of the R 1⁄4 45–60 kpc
\nannulus, A2589 possesses a remarkably symmetrical X-ray image and is therefore an exceptional candidate for precision
\nstudies of its mass profile by applying hydrostatic equilibrium. The total gravitating matter profile is well described
\nby the NFW model with cvir 1⁄4 6:1 0:3 and Mvir 1⁄4 3:3 0:3 ; 1014 M (rvir 1⁄4 1:74 0:05 Mpc), in
\nexcellent agreement with CDM. When the mass of the hot intracluster medium is subtracted from the gravitating
\nmatter profile, the NFW model fitted to the resulting dark matter (DM ) profile produces essentially the same result.
\nHowever, when accounting for the stellar mass (M) of the cD galaxy, the NFW fit to the DM profile substantially
\ndegrades in the central r 50 kpc for reasonable values of M /LV . Modifying the NFW DM halo by adiabatic
\ncontraction arising from the early condensation of stellar baryons in the cD galaxy further degrades the fit. The fit is
\nimproved substantially with a Se ́rsic-like model recently suggested by high-resolution N-body simulations but with
\nan inverse Se ́rsic index, 0:5, that is a factor of 3 higher than predicted. We argue that neither random turbulent
\nmotions nor magnetic fields can provide sufficient nonthermal pressure support to reconcile the XMM-Newton mass
\nprofile with adiabatic contraction of a CDM halo, assuming reasonable values of M /LV . Our results support the
\nscenario in which, at least for galaxy clusters, processes during halo formation counteract adiabatic contraction so that
\nthe total gravitating mass in the core approximately follows the NFW profile.